Method and apparatus for controlling combustion in a combustion boiler

ABSTRACT

A technique for controlling the combustion of fuel in a combustion boiler, comprising at least the following steps: a) a desired combustion air quantity for the combustion of the fuel in the combustion boiler is determined, b) a combustion air quantity which is available for the combustion of the fuel in the combustion boiler is determined, c) at least one combustion air inflow is controlled by at least one material output opening or at least one appliance opening in the combustion boiler, in order to at least partially match the combustion air quantity available in the combustion boiler to the desired combustion air quantity.

The present invention relates to a method and a device for controlling a combustion of fuel in a combustion boiler. The invention can be used in particular in combustion boilers of fossil-fired power plants.

The prior art discloses combustion boilers having at least one combustion chamber in which fuel is burned with a feed of combustion air. During the combustion of the fuels, hot combustion gases are generated, the heat energy of which is extracted in exhaust-gas-conducting regions of the combustion boiler, in particular by means of heat exchangers, and is subsequently converted into electrical energy. Increasingly stringent pollutant limits must be adhered to for the combustion of fuels in combustion-type power plants. Aside from the retroactive purification of the combustion exhaust gases, for example by means of filters, the prevention of the generation of pollutants during the combustion of the fuels is of particular importance.

In order, during the combustion of fuels, to generate combustion exhaust gases which contain the least amount of pollutants possible, extremely precise control of the oxygen available in a combustion chamber for a combustion is desirable, the quantity of said oxygen being dependent in particular on the mass and the quality of the fuel used in the combustion chamber. In the known combustion boilers, therefore, a controlled supply of oxygen-containing combustion air into the combustion chamber takes place via corresponding combustion air supplies.

It is also known for at least one conveyor to be provided below a material discharge opening for the removal of combustion residues from the combustion chamber, by means of which conveyor the hot ashes and/or other combustion residues are removed from the combustion boiler. For the operation of such conveyors, it has also already been proposed to bring a cooling-air flow and/or oxidation-gas flow into contact with the ashes counter to the conveying direction in order to burn unburned (and incompletely burned) constituents on the conveyor itself and if appropriate to achieve a complete solidification of the ashes before they are discharged from the conveyor. Here, said cooling-air flow or oxidation-gas flow is severely limited because it passes through the material discharge opening owing to a negative pressure (which often exists) in the combustion chamber. Such a conveyor is described for example in WO-A-2010043504.

It has now been identified that, in particular under fluctuating load conditions in the combustion boiler and/or at the conveyor, undesired influence is exerted on the desired result of the combustion and/or of the conveying, cooling and post-combustion of the ashes.

It is therefore an object of the invention to at least partially solve the problems highlighted with regard to the prior art and in particular to specify a method for controlling a combustion of fuel in a combustion boiler, by means of which method the combustion air available in the combustion chamber for the combustion of the fuel can be controlled particularly precisely. Furthermore, it is also sought to specify a combustion boiler by means of which the combustion air available in a combustion chamber for the combustion of the fuel can be controlled in a particularly precise manner. It is also sought to achieve that, despite varying load conditions in the combustion boiler and/or in the conveyor, an improved result can be realized with regard to at least one of the following aspects: exhaust-gas composition, temperature of the combustion and/or of the ashes, stoichiometry of the combustion, cooling of the ashes, post-combustion of the ashes, heat recovery.

Said objects are achieved by means of a method according to the features of patent claim 1 and a device according to the features of patent claim 6. Further advantageous refinements of the invention are specified in the dependent patent claims. It should be pointed out that the features specified individually in the dependent patent claims may be combined with one another in any desired technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the patent claims are rendered more precisely and explained in more detail in the description, with further preferred refinements of the invention being presented.

The method according to the invention for controlling a combustion of fuel in a combustion boiler has at least the following steps:

a) determining a desired combustion air quantity for the combustion of the fuel in the combustion boiler,

b) determining an available combustion air quantity for the combustion of the fuel in the combustion boiler,

c) controlling at least one combustion air inflow through at least one material discharge opening or an apparatus opening of the combustion boiler in order to at least partially align the available combustion air quantity in the combustion boiler with the desired combustion air quantity.

Here, the expression “combustion air” is to be understood to mean a gas or gas mixture which comprises at least oxygen. The oxygen content of the combustion air is in particular at least 10 vol. % (per cent by volume), preferably at least 20 vol. % or particularly preferably at least 30 vol. %. The combustion air may in particular also be, if appropriate pre-heated, ambient air. The desired combustion air quantity is in particular that combustion air quantity which, for the respective type and/or quantity of fuel to be burned in the combustion chamber, provides an oxygen quantity required for a particularly advantageous, in particular low-emission, combustion of the fuel. The desired combustion air quantity may in particular also be that combustion air quantity which, depending on the oxygen content of the combustion air, is required for a stoichiometric combustion of the fuel in the combustion chamber. As fuels, use may be made in particular of brown coal, mineral coal, mineral oil, natural gas, household waste, industrial waste and/or biomass. The respectively desired combustion air quantity, which is dependent on the type, mass and/or quality of the fuel, is basically known to a person skilled in the art and emerges in particular from relevant operating manuals for the combustion boiler. For the determination of the desired (or required) combustion air quantity, use may be made of measurement values and/or mathematical models, such that the combustion air quantity required for the predefined (stoichiometric) combustion at a (present or predetermined future) point in time can be determined.

According to the proposed method, the combustion air quantity actually available in the combustion boiler is furthermore determined, for example by means of an oxygen sensor which measures an oxygen concentration within a combustion chamber of the combustion boiler. It is self-evidently also possible for this purpose for use to be made of other sensors and/or mathematical models etc. In this respect, a determination of the combustion air quantity actually available in the combustion boiler (presently or at a predetermined point in time) may be performed by means of measurement values and/or calculation. Said step b) may in particular be performed after and/or during and/or before step a).

An alignment of the available combustion air quantity in the combustion chamber with the desired combustion air quantity in the combustion chamber then takes place. In other words, the available combustion air quantity in the combustion chamber should be set as precisely as possible to the desired combustion air quantity in the combustion chamber. This is achieved through control (in particular regulation) of at least one combustion air inflow through at least one material discharge opening and/or at least one apparatus opening of the combustion boiler. An “apparatus opening” is to be understood to mean in particular an inlet (for example through the side wall and/or the top wall) to the combustion boiler, via which inlet additional air is (at least intermittently) supplied (in an undefined manner). This includes in particular those openings through which apparatuses, such as for example sensors, cleaning systems, sample extraction units etc., are (intermittently) introduced into the combustion boiler (and/or downstream regions). If appropriate, seal elements may also be provided there, which seal elements use a scavenging gas.

This means in particular that the at least one combustion air inflow through the at least one material discharge opening and/or at least one apparatus opening and/or the provided combustion air supply of the combustion boiler are/is (actively) reduced and/or increased and/or (under fluctuating ambient conditions) kept constant in order to align the available combustion air quantity in the combustion chamber as precisely as possible with the desired combustion air quantity in the combustion chamber. The combustion air inflow is at least partially a combustion air quantity which flows into the combustion chamber through the material discharge opening of the combustion chamber. The combustion air quantity is for example measured in m³/min (cubic meters per minute). It must be clarified here that the alignment of the available combustion air quantity in the combustion chamber with the desired combustion air quantity in the combustion chamber may additionally also be realized by means of further combustion air supplies of the combustion chamber (for example separate burners, nozzles etc. in the wall of the combustion boiler). The control of the at least one combustion air inflow through the at least one material discharge opening and/or apparatus opening thus constitutes an, if appropriate additional, regulating variable for aligning the available combustion air quantity in the combustion chamber with the desired combustion air quantity in the combustion chamber in a particularly precise manner.

It is also pointed out that the at least one material discharge opening of the combustion chamber is an opening in the combustion chamber from which combustion residues of the fuel are at least partially and/or substantially completely removed from the combustion chamber. The material discharge opening is preferably formed in a base region of the combustion chamber and connects the combustion chamber in particular to a conveyor, arranged below the combustion boiler, for combustion residues.

The alignment preferably takes place regularly during the operation of the combustion boiler, in particular when at least one parameter relevant for the combustion and/or for the conveying of the ashes changes. In the first case, this means for example that the alignment takes place if the fuel and/or the ambient conditions in the combustion boiler change. In the second case, this means in particular that the ash quantity, the cooling power and/or the degree of post-combustion is changed. The alignment very particularly preferably takes place practically in real time, such that the operation is adapted or newly set very quickly.

It has now been identified that gases can flow into the combustion chamber in (temporally) significantly varying quantities and/or in large amounts via said material discharge opening and/or apparatus opening, and therefore the oxygen available in the combustion chamber for the combustion of the fuel cannot be added with the accuracy desired for adhering to very low pollutant limits. It has duly been attempted to limit an inflow of combustion air through material discharge openings and/or apparatus openings of the combustion chamber to a minimum, but the nevertheless present uncontrolled inflow of combustion air out of material discharge openings and/or apparatus openings of the combustion chamber is, as before, associated with considerable uncertainties with regard to precise control of the oxygen available in the combustion chamber for the combustion of the fuel. Furthermore, it has thus been necessary, if appropriate, for the power or effectiveness of the combustion boiler and/or of the conveyor to be reduced in order to avoid said disruptive influences. This problem, which has existed for a long time, has now been solved.

The invention is accordingly based in particular on the concept that all of the air flows and/or gas flows (insofar as they have an effect on the combustion process) entering the boiler are detected and taken into consideration for the adjustment of the combustion air made available. It is then possible for the air flow via the classic combustion air supply, the material discharge opening and/or the apparatus opening to be adapted in a demand-oriented and/or application-oriented manner. This on-line regulation of the combustion air via all of the openings permits a particularly precise and possibly also directional supply of combustion air, which can advantageously influence the position of the flame and/or the effectiveness of the combustion process and/or the formation of residues/pollutants/etc.

In said method, it is accordingly particularly preferable for step c) to comprise an active adaptation of the overall combustion air quantity. This refers in particular to direct, so-called “on-line” regulation. Here, measurement values and/or characteristic values, for example, of the combustion boiler are determined (including by means of sensors) and are directly processed (in real time, for example using corresponding regulating software) such that a prompt and immediate adaptation of the combustion air quantity made available is performed, which corresponds practically exactly to the desired combustion air quantity.

Here, the method is preferably carried out such that at least one of the following combustion air inflows is regulated in a manner dependent on step c):

-   -   combustion air inflow via the combustion air supply,     -   combustion air inflow via the at least one material discharge         opening,     -   combustion air inflow via the at least one apparatus opening.

Here, during the operation of the combustion boiler, a different combustion air inflow in each case may be increased, lowered and/or kept constant at different points in time; if appropriate, it is also possible for a plurality of combustion air inflows to be adapted simultaneously. It is possible in particular for the magnitude and manner of the change of the combustion air inflow to be selected; it is for example possible for similar apparatus openings to be opened or closed alternately, or for the scavenging gas thereof to be operated in an adapted manner. However, if for example the discharge from the combustion boiler changes significantly, an adaptation of the (primary/secondary) combustion air supply and/or of the material discharge opening may be performed.

It is preferable if, in step c), the combustion air inflow is controlled at least by way of one of the following means:

-   -   at least one dosing device for combustion air at the at least         one material discharge opening of the combustion boiler,     -   at least one conveyor for combustion residues,     -   at least one at least partially closable opening in at least one         housing of the at least one conveyor.

The at least one dosing device for combustion air at the at least one material discharge opening in particular comprises at least partially and/or fully closable flaps and/or at least partially and/or fully closable valves in the region of the at least one material discharge opening of the combustion chamber of the combustion boiler, by means of which flaps and/or valves the admission of a combustion air inflow into the combustion boiler from the outside can be controlled. Here, a reduction of the combustion air inflow is realized by means of at least partial or complete closure of the material discharge opening by the dosing device and/or an increase of the combustion air inflow is realized by means of at least partial or complete opening of the material discharge opening by the dosing device.

In addition or alternatively, the combustion air inflow may also be controlled by means of at least one conveyor for combustion residues, for example by virtue of a conveying speed of the conveyor being adapted, such that in particular the material discharge opening of the combustion chamber is at least partially or completely closed off by combustion residues. Furthermore, the loading height of the conveyor with combustion residues may be influenced by virtue of the flow resistance to be overcome by the combustion air inflow, in particular in the region of the material discharge opening, being influenced. It is thus possible, for example, for the combustion air inflow to be reduced by means of a reduction of the conveying speed of the at least one conveyor or to be reduced by means of an increase of the conveying speed of the at least one conveyor.

The at least one conveyor for combustion residues is preferably arranged below the at least one material discharge opening and substantially surrounded by at least one housing which is connected in a substantially gas-tight fashion to the combustion boiler. Said at least one housing has an at least partially and/or fully closable opening, wherein said opening may in particular be an opening of the housing at the end of a conveying path of the conveyor, in particular via which combustion residues conveyed on the conveyor are removed from and/or out of the conveyor and/or out of the at least one housing of the at least one conveyor. From said at least one partially and/or fully closable opening, ambient air can flow into the housing, form a flow path within the at least one housing along the at least one conveyor, and flow through the at least one material discharge opening into the combustion chamber of the combustion boiler, as a combustion air inflow. Said process may for example be assisted by means of one or more pumps, fans, valves etc. in the region of the at least one at least partially closable opening and/or along the flow path of the combustion air inflow. The at least one opening of the housing is partially and/or completely closable, such that the combustion air inflow entering the combustion chamber through the housing and the material discharge opening can be controlled. It must however be clarified that further openings of the housing, for example openings for the targeted supply of cooling air for the combustion residues conveyed by the at least one conveyor, may also be designed to be closable in order to correspondingly control the combustion air inflow through the at least one material discharge opening of the combustion boiler.

With the means proposed here, it is sought in particular to firstly make available a suitable air quantity for the operation of the conveyor, such that for example a desired degree of combustion and/or degree of solidification of the discharged combustion residues is maintained. Furthermore, if the air quantity required for this purpose is relatively large, the admission into the combustion boiler through the material discharge opening should subsequently be limited, and/or the combustion air quantity supplied at other locations should be adapted. This, too, takes place practically in real time, in particular by means of corresponding monitoring measures and regulation measures.

It is preferable if at least one physical characteristic of the combustion air inflow is measured by means of at least one second sensor or the determination of the available combustion air quantity is performed by means of at least one first sensor. Said measures may self-evidently be combined with one another.

The at least one physical characteristic of the combustion air inflow may be for example the mass flow rate, the volume flow rate, a temperature, the humidity, a chemical composition, an oxygen concentration and/or some other physical characteristic of the combustion air inflow flowing through the at least one material discharge opening which has an influence on the combustion of the fuel in the combustion chamber of the combustion boiler. The at least one second sensor is in particular a sensor by means of which at least one of the abovementioned physical characteristics of the combustion air inflow can be determined. The at least one first sensor is consequently for example an oxygen sensor which can measure an oxygen concentration within the at least one combustion chamber of the combustion boiler. The measurement of the at least one physical characteristic of the combustion air inflow and/or the determination of the available combustion air quantity by means of the first sensor and/or second sensor preferably takes place continuously, such that, if a deviation of the available combustion air quantity in the combustion chamber from the desired combustion air quantity in the combustion chamber is detected, the at least one combustion air inflow can be controlled, that is to say reduced or increased, as promptly as possible.

According to a further aspect of the invention, there is also proposed a combustion boiler, having at least one combustion chamber for fuel, at least one material discharge opening for the discharge of combustion residues, at least one first sensor for determining a combustion air quantity available in the at least one combustion chamber for the combustion of the fuel, at least one second sensor for at least one physical characteristic of of a combustion air inflow through the at least one material discharge opening, wherein the at least one material discharge opening has at least one dosing device for the combustion air inflow and/or at least one housing which at least partially surrounds at least one conveyor for combustion residues and which has at least one at least partially closable opening. The combustion boiler proposed here is provided in particular for carrying out the method according to the invention for controlling a combustion of fuel in a combustion boiler. Reference is therefore made at this juncture to the description of the method according to the invention.

It is preferable in this context for the housing to have a plurality of openings which are all closable. With regard to the dosing device, it may also be provided that, the latter, a part of the combustion air flow provided via the conveyor is extracted again (for example by means of a corresponding suction device). In this respect, it is also possible for a dosing device and a conveyor to be realized jointly with the combustion boiler.

In a further expedient embodiment, the at least one first sensor, the at least one second sensor, the at least one dosing device, at least one drive of the at least one conveyor, a combustion air supply of the combustion chamber and/or at least one of the at least partially closable openings of the housing are/is connected in data-transmitting fashion to a control unit, wherein the control unit is set up to regulate a combustion air inflow through the at least one material discharge opening.

This permits particularly simple automated control, that is to say in particular particularly simple automated control and/or regulation, of the at least one combustion air inflow flowing through the at least one material discharge opening. The at least one drive of the at least one conveyor is for example an electric motor by means of which a conveying speed of the conveyor can be varied.

The invention and the technical field will be explained in more detail below on the basis of the figure. It is pointed out that the figure shows a particularly preferred design variant of the invention, to which the invention is however not restricted.

FIG. 1 schematically shows a combustion boiler 2 with a combustion chamber 11. A combustion of fuel 1 takes place, with a feed of combustion air via a (primary/secondary) combustion air supply 15, within the combustion chamber 11. The combustion boiler 2 also has a plurality of apparatus openings 19 through which an additional air flow can (intermittently and/or permanently) enter, for example if sensors and/or cleaning units are led through and/or operated there. The combustion chamber 11 of the combustion boiler 2 also has a material discharge opening 3 via which combustion residues 6 can be removed from the combustion chamber 11 onto a conveyor 5 arranged below the material discharge opening 3. The conveyor 5 is in this case formed as a belt-type conveyor. For the control of a combustion air inflow 16, there is arranged in the region of the material discharge opening 3 a dosing device 4 which, in this case, is in the form of two rotatably mounted flaps. The combustion air inflow is reduced by closing the dosing device 4 and increased by opening the dosing device 4. The combustion boiler 2 also has, in the combustion chamber 11, a first sensor 9 for determining an available combustion air quantity in the combustion boiler 2, and a second sensor 10 for determining a physical characteristic of the combustion air inflow 16 in the region of the material discharge opening 3.

Aside from the dosing device 4, the combustion air inflow 16 can also be controlled by means of a drive 12 of the conveyor 5, in particular by means of an adaptation of a conveying speed of the conveyor 5 and thus a loading height 17 of the conveyor 5.

The conveyor 5 is furthermore arranged in a housing 8 which, in this exemplary embodiment, has two at least partially and/or fully closable openings 7. The lower of the two at least partially and/or fully closable openings 7 can be at least partially and/or fully closed by means of an adjustable flap 14. Ambient air flows into the housing 8 through the two partially and/or fully closable openings 7 and forms a flow path 18 along the conveyor 5 in the direction of the combustion chamber 11. The ambient air in the housing 8 can at least partially cool the combustion residues 6 on the conveyor 5 and at least partially assist a post-combustion of the combustion residues 6 on the conveyor 5, wherein at least a part of the oxygen is extracted from the ambient air by the post-combustion of the combustion residues 6 on the conveyor 5. This means that the oxygen concentration of the ambient air at least partially decreases in the direction of the combustion chamber 11. The first sensor 9, the second sensor 10, the dosing device 4, the drive 12, the combustion air supply 15 and/or the flap 14 are (as indicated here by dashed lines) connected in data-transmitting fashion to a control unit 13 which is set up to control the combustion air inflow 16 in order to at least partially or fully align the available combustion air quantity, that is to say in particular the available oxygen quantity, in the combustion boiler 2 with the desired combustion air quantity, that is to say in particular the desired oxygen quantity.

The invention is characterized by particularly precise regulation of the available combustion air quantity in the combustion boiler and makes it possible for the pollutants generated during the combustion of fuels to be particularly advantageously reduced, wherein very good (complete) treatment of the discharged combustion residues can simultaneously be ensured.

LIST OF REFERENCE NUMERALS

-   1 Fuel -   2 Combustion boiler -   3 Material discharge opening -   4 Dosing device -   5 Conveyor -   6 Combustion residues -   7 Closable opening -   8 Housing -   9 First sensor -   10 Second sensor -   11 Combustion chamber -   12 Drive -   13 Control unit -   14 Flap -   15 Combustion air supply -   16 Combustion air inflow -   17 Loading height -   18 Flow path -   19 Apparatus opening 

1. A method for controlling combustion of fuel in a combustion boiler, having at least the following steps: a) determining a desired combustion air quantity for the combustion of the fuel in the combustion boiler, b) determining an available combustion air quantity for the combustion of the fuel in the combustion boiler, c) controlling at least one combustion air inflow through at least one material discharge opening or at least one apparatus opening of the combustion boiler in order to at least partially align the available combustion air quantity in the combustion boiler with the desired combustion air quantity.
 2. The method as claimed in claim 1, wherein step c) comprises an active adaptation of the entire combustion air quantity.
 3. The method as claimed in claim 1, wherein at least one of the following combustion air inflows is regulated in a manner dependent on step c): combustion air inflow via the combustion air supply, combustion air inflow via the at least one material discharge opening, combustion air inflow via the at least one apparatus opening.
 4. The method as claimed in claim 1, wherein, in step c), the control of the combustion air inflow is realized at least by way of one of the following: at least one dosing device for combustion air at the at least one material discharge opening of the combustion boiler, at least one conveyor for combustion residues, at least one at least partially closable opening in at least one housing of the at least one conveyor.
 5. The method as claimed in claim 1, wherein at least one physical characteristic of the combustion air in-flow is measured by means of at least one second sensor or the determination of the available combustion air quantity is performed by means of at least one first sensor.
 6. A combustion boiler, having at least one combustion chamber for fuel, at least one material discharge opening for the discharge of combustion residues, at least one first sensor for determining a combustion air quantity available in the at least one combustion chamber for the combustion of the fuel, at least one second sensor for at least one physical characteristic of a combustion air inflow through the at least one material discharge opening, wherein the at least one material discharge opening has at least one dosing device for the combustion air inflow or at least one housing which at least partially surrounds at least one conveyor for combustion residues and which has at least one at least partially closable opening.
 7. The combustion boiler as claimed in claim 6, wherein the at least one first sensor, the at least one second sensor, the at least one dosing device, at least one drive of the at least one conveyor or at least one of the at least partially closable openings of the housing is connected in data-transmitting fashion to a control unit wherein the control unit is set up to regulate a combustion air inflow through the material discharge opening. 